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1.
Nanotechnology ; 32(7): 075707, 2021 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-33120365

RESUMO

High thermal conductivity is an important parameter for nitride-based power electronic and deep-UV light emitters. Especially in the latter case short period superlattices and multicomponent alloys are used and the knowledge of the thermal properties of the binary compounds is sufficient. In-plane and cross-plane thermal conductivity of AlGaN/GaN superlattices were measured by differential two-wire 3ω method in the temperature range from 147 to 325 K. Samples were grown by metalorganic vapor phase epitaxy; the structure quality and accuracy of superlattice structures preparation were verified by means of HRXRD and transmission electron microscopy. It was observed, that value of thermal conductivities decrease with decreasing period thickness, while temperature dependencies differ from each other-in-plane thermal conductivity decreases, and cross-plane-increases with increasing temperature. Callaway method was used for thermal conductivity calculation; dependence of boundary scattering rate on the phonon wavelength was taken into account. Minimum thermal conductivity was added to calculated values to include the influence of high frequency acoustic phonons and optical phonons on the heat transport. Calculations are in good agreement with experimental results.

2.
Toxicon ; 151: 74-78, 2018 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-29890231

RESUMO

In the American continent, larval forms (caterpillars) of the Lonomia genus can cause systemic reactions in human beings. In this Paper, we report the third case of Lonomia envenoming recorded in French Guiana in 25 years, and the first in which specific antivenom was administered. Severe symptoms of the envenoming were observed in our patient including pain; coagulopathy and systemic hemorrhage. They are caused by skin contact with caterpillars. Recovery, however, was quite satisfactory thanks to the international cooperation of the health authorities in both France and Brazil.


Assuntos
Antivenenos/uso terapêutico , Venenos de Artrópodes/toxicidade , Transtornos da Coagulação Sanguínea/induzido quimicamente , Transtornos da Coagulação Sanguínea/tratamento farmacológico , Mordeduras e Picadas de Insetos/tratamento farmacológico , Mariposas/fisiologia , Animais , Brasil , Feminino , Guiana Francesa , Humanos , Mordeduras e Picadas de Insetos/patologia , Larva/fisiologia , Pessoa de Meia-Idade
3.
Nanotechnology ; 28(50): 505710, 2017 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-29064371

RESUMO

We studied the emission of bare and aluminum quinoline (Alq3)/gold coated wurtzite GaN nanorods by temperature- and intensity-dependent time-integrated and time-resolved photoluminescence (PL). The GaN nanorods of ∼1.5 µm length and ∼250 nm diameter were grown by plasma-assisted molecular beam epitaxy. Gold/Alq3 coated GaN nanorods were synthesized by organic molecular beam deposition. The near band-edge and donor-acceptor pair luminescence was investigated in bare GaN nanorods and compared with multilevel model calculations providing the dynamical parameters for electron-hole pairs, excitons, impurity bound excitons, donors and acceptors. Subsequently, the influence of a 10 nm gold coating without and with an Alq3 spacer layer was studied and the experimental results were analyzed with the multilevel model. Without a spacer layer, a significant PL quenching and lifetime reduction of the near band-edge emission is found. The behavior is attributed to surface band-bending and Förster energy transfer from excitons to surface plasmons in the gold layer. Inserting a 5 nm Alq3 spacer layer reduces the PL quenching and lifetime reduction which is consistent with a reduced band-bending and Förster energy transfer. Increasing the spacer layer to 30 nm results in lifetimes which are similar to uncoated structures, showing a significantly decreased influence of the gold coating on the excitonic dynamics.

4.
Sci Rep ; 7: 41877, 2017 02 02.
Artigo em Inglês | MEDLINE | ID: mdl-28150798

RESUMO

The Fermi level position in (Ga,Mn)N has been determined from the period-analysis of GaN-related Franz-Keldysh oscillation obtained by contactless electroreflectance in a series of carefully prepared by molecular beam epitaxy GaN/Ga1-xMnxN/GaN(template) bilayers of various Mn concentration x. It is shown that the Fermi level in (Ga,Mn)N is strongly pinned in the middle of the band gap and the thickness of the depletion layer is negligibly small. For x > 0.1% the Fermi level is located about 1.25-1.55 eV above the valence band, that is very close to, but visibly below the Mn-related Mn2+/Mn3+ impurity band. The accumulated data allows us to estimate the Mn-related band offsets at the (Ga,Mn)N/GaN interface. It is found that most of the band gap change in (Ga,Mn)N takes place in the valence band on the absolute scale and amounts to -0.028 ± 0.008 eV/% Mn. The strong Fermi level pinning in the middle of the band gap, no carrier conductivity within the Mn-related impurity band, and a good homogeneity enable a novel functionality of (Ga,Mn)N as a semi-insulating buffer layers for applications in GaN-based heterostuctures.

5.
J Phys Condens Matter ; 28(26): 265302, 2016 07 06.
Artigo em Inglês | MEDLINE | ID: mdl-27173643

RESUMO

We present a comparative study of two self-assembled quantum dot (QD) systems based on II-VI compounds: CdTe/ZnTe and CdSe/ZnSe. Using magneto-optical techniques we investigated a large population of individual QDs. The systematic photoluminescence studies of emission lines related to the recombination of neutral exciton X, biexciton XX, and singly charged excitons (X(+), X(-)) allowed us to determine average parameters describing CdTe QDs (CdSe QDs): X-XX transition energy difference 12 meV (24 meV); fine-structure splitting δ1=0.14 meV (δ1=0.47 meV); g-factor g = 2.12 (g = 1.71); diamagnetic shift γ=2.5 µeV T(-2) (γ =1.3 µeV T(-2)). We find also statistically significant correlations between various parameters describing internal structure of excitonic complexes.

7.
Clin Microbiol Infect ; 18(7): E221-31, 2012 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-21958195

RESUMO

Atypical Toxoplasma gondii strains, unrelated to archetypal clonal lineages (I, II, III), have been reported more frequently over the last decade in areas other than Europe and North America. A newly described form of toxoplasmosis, 'Amazonian toxoplasmosis' (AT), has been reported since 2002 in French Guiana. It is characterized by severe cases and atypical strains linked to a neotropical forest-based cycle. We report on the cases of AT that required intensive care management. We performed a prospective observational study on hospitalized adults in the Intensive Care Unit (ICU) from 2002 to 2008. Clinical and laboratory data, microbiological findings and outcomes were recorded. Data, including the ICU simplified acute physiology score and the pneumonia severity index, were calculated. Epidemiological risk factors for AT were assessed through questionnaires. Eleven non-immunodeficient patients were admitted to the ICU in Cayenne for life-threatening pneumonia associated with disseminated toxoplasmosis. Mechanical ventilation was necessary in seven patients, four of whom required immediate orotracheal intubation. Cardiac and ophthalmological abnormalities were found in five and four patients, respectively. One patient died from multiple organ failure. The genetic characterization of Toxoplasma DNA using six microsatellite markers revealed unique and atypical genotypes in eight patients. All patients presented epidemiological risk factors for AT. In French Guiana, significant T. gondii-related infectious syndrome associated with the lungs, a high level of LDH activity and the reported risk factors for AT was strongly suggestive of disseminated toxoplasmosis with a possible trend toward life-threatening pneumonia.


Assuntos
Toxoplasma/isolamento & purificação , Toxoplasmose/patologia , Adolescente , Adulto , DNA de Protozoário/genética , Feminino , Guiana Francesa/epidemiologia , Genótipo , Humanos , Unidades de Terapia Intensiva , Masculino , Repetições de Microssatélites , Estudos Prospectivos , Fatores de Risco , Índice de Gravidade de Doença , Inquéritos e Questionários , Análise de Sobrevida , Toxoplasma/classificação , Toxoplasma/genética , Toxoplasmose/epidemiologia , Toxoplasmose/mortalidade , Toxoplasmose/parasitologia , Adulto Jovem
8.
Nanotechnology ; 22(26): 265202, 2011 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-21576780

RESUMO

We report on the fabrication of a light-emitting diode based on GaN nanorods containing InGaN quantum wells. The unique system consists of tilted N-polar nanorods of high crystalline quality. Photoluminescence, electroluminescence, and spatially resolved cathodoluminescence investigations consistently show quantum well emission around 2.6 eV. Scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy measurements reveal a truncated shape of the quantum wells with In contents of (15 ± 5)%.

9.
Nanotechnology ; 22(2): 025603, 2011 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-21139192

RESUMO

GaN nanorods were grown on r-plane sapphire substrates by a two-step approach. Nucleation sites for the nanorods were provided by the formation of AlN islands during nitridation in a metal organic vapor phase system. These islands are a-plane oriented as expected for nitride growth on r-plane sapphire. The nanorods themselves were grown by plasma assisted molecular beam epitaxy. The nanorods show an inclination towards the surface normal of 28.3° and are highly ordered. Studies with high resolution x-ray diffraction polar plots reveal the epitaxial relationship between the substrate and nanorods as a c-direction growth on inclined m-plane facets of the nitridated islands. The determined lattice constants show nanorods which are strain free. The growth direction of the nanorods has been confirmed in a transmission electron microscope by convergent beam electron diffraction patterns to be in the N-polar [Formula: see text] direction.

10.
Nanotechnology ; 21(1): 015204, 2010 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-19946174

RESUMO

We present electrically driven luminescence from single InGaN quantum dots embedded into a light emitting diode structure grown by metal-organic vapor-phase epitaxy. Single sharp emission lines in the green spectral region can be identified. Temperature dependent measurements demonstrate thermal stability of the emission of a single quantum dot up to 150 K. These results are an important step towards applications like electrically driven single-photon emitters, which are a basis for applications incorporating plastic optical fibers as well as for modern concepts of free space quantum cryptography.

11.
Phys Rev Lett ; 102(23): 235501, 2009 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-19658946

RESUMO

The optical signatures of Mg-related acceptors in GaN have been revisited in samples specifically grown on bulk GaN templates, to avoid strain broadening of the optical spectra. Bound-exciton spectra can be studied in these samples for Mg concentrations up to [Mg] approximately 2 x 10(19) cm(-3). Contrary to previous work it is found that instabilities in the photoluminescence spectra are not due to unstable shallow donors, but to unstable Mg-related acceptors. Our data show that there are two Mg-related acceptors simultaneously present: the regular (stable) substitutional Mg acceptor, and a complex acceptor which is unstable in p-GaN.

12.
Nature ; 460(7252): 245-9, 2009 Jul 09.
Artigo em Inglês | MEDLINE | ID: mdl-19587766

RESUMO

Lasers are recognized for coherent light emission, the onset of which is reflected in a change in the photon statistics. For many years, attempts have been made to directly measure correlations in the individual photon emission events of semiconductor lasers. Previously, the temporal decay of these correlations below or at the lasing threshold was considerably faster than could be measured with the time resolution provided by the Hanbury Brown/Twiss measurement set-up used. Here we demonstrate a measurement technique using a streak camera that overcomes this limitation and provides a record of the arrival times of individual photons. This allows us to investigate the dynamical evolution of correlations between the individual photon emission events. We apply our studies to micropillar lasers with semiconductor quantum dots as the active material, operating in the regime of cavity quantum electrodynamics. For laser resonators with a low cavity quality factor, Q, a smooth transition from photon bunching to uncorrelated emission with increasing pumping is observed; for high-Q resonators, we see a non-monotonic dependence around the threshold where quantum light emission can occur. We identify regimes of dynamical anti-bunching of photons in agreement with the predictions of a microscopic theory that includes semiconductor-specific effects.

13.
J Synchrotron Radiat ; 16(Pt 4): 494-7, 2009 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-19535863

RESUMO

The local structure around the indium atoms in uncapped and capped In(x)Ga(1-x)N quantum dots has been studied by In K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. The samples were grown by metal organic vapour phase epitaxy. The EXAFS was successfully applied to study the structural properties of buried quantum dots which are not optically active. The analysis revealed that capping the quantum dots with GaN does not affect the bond distances of the In-N and In-Ga, but makes the In-In distance shorter by 0.04 A.

14.
Nanotechnology ; 20(1): 015401, 2009 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-19417251

RESUMO

A II-VI wide-bandgap resonant cavity light-emitting diode is presented. The active region consists of CdSe quantum dots embedded in ZnSSe/MgS barriers, resulting in improved quantum efficiency at elevated temperatures. The resonant cavity is formed by a 14-period bottom distributed Bragg reflector and the semiconductor to air interface on top of the structure. Temperature dependent micro-electroluminescence measurements reveal emission of a single quantum dot up to 90 K. The turn-on voltages are 6 V at 4 K and 4 V at room temperature. These results are promising for the realization of green surface-emitting devices in general, and especially for an electrically driven prospective single photon source operating at room temperature.

15.
Nanotechnology ; 20(7): 075604, 2009 Feb 18.
Artigo em Inglês | MEDLINE | ID: mdl-19417425

RESUMO

Self-organized and highly ordered GaN nanorods were grown without catalyst on r-plane sapphire using a combination of molecular beam epitaxy and metal-organic vapor-phase epitaxy. AlN nucleation centers for the nanorods were prepared by nitridation of the sapphire in a metal-organic vapor-phase epitaxy reactor, while the nanorods were grown by molecular beam epitaxy. A coalesced two-dimensional GaN layer was observed between the nanorods. The nanorods are inclined by 62 degrees towards the [Formula: see text]-directions of the a-plane GaN layer. The high degree of ordering and the structural perfection were confirmed by micro-photoluminescence measurements.

18.
Phys Rev Lett ; 90(21): 216601, 2003 May 30.
Artigo em Inglês | MEDLINE | ID: mdl-12786578

RESUMO

Quantum interference of one- and two-photon excitation of unbiased semiconductors yields ballistic currents of carriers. The magnitudes and directions of the currents and the spin orientations of the carriers are controlled by the polarization and relative phase of the exciting femtosecond laser fields. We provide direct experimental evidence for the spin polarization of the optically injected spin currents by detecting a phase-dependent spatial shift of the circularly polarized photoluminescence in cubic ZnSe.

19.
Phys Rev Lett ; 89(17): 177403, 2002 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-12398705

RESUMO

We demonstrate the generation of triggered single photons at a predetermined and well defined energy using the radiative recombination of single nitrogen-bound excitons in a semiconductor. The nitrogen atoms are embedded in a ZnSe quantum well structure and were excited by nonresonant optical pumping (82 MHz) at low temperature (4 K). We find resolution-limited photoluminescence lines (280 micro eV) which display photon antibunching under continuous optical pumping. Our results also suggest that single nitrogen-bound excitons are well suited for cavity quantum electrodynamics experiments.

20.
J Infect Dis ; 184(3): 278-84, 2001 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-11443552

RESUMO

The annual incidence of Q fever in French Guiana was found to have increased in 1996 and was 37/100,000 population over the last 4 years. Subsequent investigations in Cayenne and its suburbs indicated that a wild reservoir of the bacteria was responsible for the epidemiologic pattern. A case-control study showed that residence near a forest and occupations and activities that result in exposure to aerosols of dusts from the soil are risk factors for Q fever. By means of time-series analysis, a strong positive correlation between rainfall and the incidence of Q fever with a time lag of 1-3 months was found. The spatial distribution of the cases showed that transmission occurs widely throughout greater Cayenne, which is incompatible with a pinpoint source of contamination. Transmission from livestock and dissemination of the bacteria by the wind appeared to be unlikely, which strengthens the hypothesis that a wild reservoir is responsible for transmission.


Assuntos
Infecções Comunitárias Adquiridas/transmissão , Reservatórios de Doenças , Febre Q/transmissão , População Suburbana , Adolescente , Adulto , Microbiologia do Ar , Animais , Animais Selvagens , Anuros , Aves , Estudos de Casos e Controles , Gatos , Criança , Pré-Escolar , Quirópteros , Infecções Comunitárias Adquiridas/diagnóstico , Infecções Comunitárias Adquiridas/epidemiologia , Coxiella burnetii/isolamento & purificação , Poeira , Feminino , Guiana Francesa/epidemiologia , Geografia , Cobaias , Humanos , Lactente , Masculino , Marsupiais , Exposição Ocupacional , Febre Q/diagnóstico , Febre Q/epidemiologia , Roedores , Estações do Ano , Microbiologia do Solo , População Urbana
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